🚀 go-pugleaf

In article <uebrt3frgh.fsf@altair.dfrc.nasa.gov>,
Richard Maine  <nospam@see.signature> wrote:
>"GerardS" <GerardS@PrairieTech.Net> writes:
>> | Richard Maine wrote:
>> |> Ron Shepard wrote:
>>
>> |> Are the exponents converted automatically with these instructions?
>> |> If they aren't, then it seems odd to be able to convert between a
>> |> double precision floating point value to a single precision value
>> |> just by loading the value into a register.
>> |
>> | Add usual caveat about my memory, but the exponents don't *NEED*
>> | converting.  I recall thinking it sort of strange the first time I saw
>> | floating point formats where the exponents weren't the same for single
>> | and double.  I've subsequently gotten used to it.  Sounds to me like
>> | you are so used to it that you didn't think of the other possibility.  :-)
>> 
>> What if the number isn't normalized ? ___________________________Gerard S.
>
>Why would it make any difference?  It doesn't that I know of.  Do you
>have something in specific in mind?

The only issue is that unusual amounts of precision can be lost
(including converting a normal range non-zero to a zero), but that
is not really a problem.

>Yes, numbers that are not normalized are prone to lose precision if
>you don't normalize them before operations.  In particular, if you
>convert a nonnormalized double to a single, you'll presumably get
>a nonnormalized single, which will have worse precision than the
>horrid IBM single format does anyway.

Yes.  If I recall, most operations prenormalised, but division didn't,
so using unnormalised numbers in divide was BAD NEWS.

>If one goes around doing operations on nonnormalized data, you are
>likely to lose precision in general.  Nothing unique to
>single-double conversion here that I see.

I am 99% certain that there was nothing special there.

>Again, I ackowledge that my memory may be confusing systems.  I
>certainly recall (with much pain) the IBM single precision floating
>point.  I get a little hazy about the details of the machine
>instruction set, though.  I did once do some BAL coding - even took a
>formal course in it, but it's been a long time (nearly 30 years) and I
>never did a lot of it.

It isn't.  My memory is fading, but it is still good enough to be
certain of that, and I have a POP in my office.


Regards,
Nick Maclaren.